Windows: Image has to come from a file, open the file on Photos app, Copy the image from the photo app and you can rightclick + paste. But its hard not being able to do this from mobile.
Pasting the image into the field will embed the image data directly into the text content of the post, you will hit the length limit very easily, so I don’t recommend doing that.
Can you share what browser you are on?
Edit: We’ve discovered the issue, it should be resolved now.